Zinc containing glasses and enamels

ABSTRACT

This invention relates to lead free, cadmium free, bismuth free low melting high durability glass and enamel compositions. The compositions comprise silica, zinc, titanium, and boron oxide based glass frits. The resulting compositions can be used to decorate and protect automotive, beverage, architectural, pharmaceutical and other glass substrates.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to, and is a continuation-in-part of,U.S. application Ser. No. 12/170,530, filed 10 Jul. 2008, now abandonedentitled “Zinc Containing Glasses and Enamels.” The entire disclosure ofthe priority application is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to low-firing, high durability glass and enamelcompositions. In particular, the invention relates to glass fritcompositions, and the glasses, ceramics and enamels made therefrom,which include ZnO, SiO₂, B₂O₃ and TiO₂. The glasses have good acidresistance, low CTE (<100×10⁻⁷) and relatively low firing temperatures(<1100° F.). All of this is achieved without the use of lead or bismuth.

2. Description of Related Art

Glass enamel compositions are well known in the art. One aim ofconventional glass and enamel compositions is the achievement of a lowfiring, high durability glass and enamel having a low coefficient ofthermal expansion (CTE). However, such glasses typically require the useof substantial amounts of relatively expensive Bi₂O₃.

Partially crystallizing glass enamel compositions that fuse atrelatively low temperatures are used, for example, to form opaquedark-colored enamel bands on the outer edges of sections of automotiveglass such as windshields and side and rear windows. These opaquedark-colored enamel bands, which typically vary in width from about 1.5cm to about 15.0 cm, greatly enhance the aesthetic appearance of thesections of glass upon which they are applied and also block thetransmission of sunlight through the glass to protect underlyingadhesives from degradation by ultraviolet radiation. Moreover, theseopaque colored enamel bands preferably have the ability to concealsilver-containing buss bars and wiring connections of rear glassdefrosting systems from view from the outside of the vehicle.

Specially formulated glass enamel compositions can be applied to planarsections of glass and fired to form opaque dark-colored enamel bands atthe same time as the bending or forming operations were performed on thesection of glass. Such glass enamel compositions can fuse and partiallycrystallize at the temperature at which a section of glass would bepreheated preparatory to a bending or forming operation. It is believedthat the partial crystallization of the enamel forms a dense, hard,protective layer that prevents the enamel from sticking to the press orvacuum head during the glass bending and transporting operations.

Although improvements have been made in recent years, the chemicaldurability of known lead-free and cadmium-free glass enamel systems usedin tableware, decorative ware, and automotive glass applications hasbeen less than desired. Further, the presence of bismuth, anincreasingly expensive metal, has been required in such formulations asa lead replacement. Therefore, a need exists for lead-free andcadmium-free (and preferably bismuth-free) enamel compositions thatexhibit excellent chemical durability to acids, water, and alkalis. Suchenamel compositions must be able to fuse and preferably, partiallycrystallize at temperatures at which sections of glass are preheatedpreparatory to forming operations so as not to stick to press or vacuumheads. Moreover, such enamel compositions should be effective inblocking ultraviolet radiation and in retarding the migration of silverand subsequent showing from overprinted buss bars and wiring connectionsof rear glass defrosting systems.

BRIEF SUMMARY OF THE INVENTION

The invention relates to a range of low firing, high durability glasses,glass frits, and glass enamel compositions. Automotive designs employ ablack glass-ceramic enamel obscuration band around the periphery ofglass windshields to hide unevenness and protect the underlying adhesivefrom ultraviolet degradation. Architectural, appliance, andcontainer/dishware glass applications often include glass ceramicmaterials for decorative purposes. Conventional low firing, highdurability enamel systems require the use of expensive bismuthborosilicate glass frits. The invention relates to a range of glassfrits including the oxides of zinc, boron, titanium and silicon. Theglass and enamel compositions fired therefrom will pass high durabilityacid testing, including, for example, performance of more than six hoursin 0.1 N H₂SO₄ at 80° C., and in many cases, performance of more than 24hours. As seen in Table 2, below, all inventive examples of the enamelsherein have performances in 0.1 N H₂SO₄ of at least 34 hours. Inaddition, crystalline seed materials including, for example zincborates, zinc titanates, aluminum silicates and others are compatiblewith the enamel compositions herein, and can yield anti-stick propertiesadvantageous in press-bend forming operations such as those used in theautomotive glass industry.

In particular, the invention provides an enamel composition comprising asolids portion comprising a frit portion, wherein the frit portioncomprises, prior to firing: (a) 38-60 wt % SiO₂, (b) 5.1-22.9 wt % B₂O₃,(c) 8.1-18 wt % TiO₂, (d) 0.1-14.9 wt % ZnO, (e) 0.1-4.5 wt % Li₂O (f)0.1-18 wt % K₂O, and (g) 1-7 wt % F.

In another embodiment, the invention involves a method of decorating asubstrate comprising: (a) applying to the substrate a coating of anenamel composition comprising a solids portion, comprising a fritportion comprising, prior to firing: (i) 38-60 wt % SiO₂, (ii) 5.1-22.9wt % B₂O₃, (iii) 8.1-18 wt % TiO₂, (iv) 0.1-14.9 wt % ZnO, (v) 0.1-3.5wt % Li₂O (vi) 0.1-18 wt % K₂O, and (vii) 1-7 wt % F, and (b) firing thesubstrate and coating at a temperature sufficient to flow the enamelcomposition to cause the enamel composition to adhere to the substrate.

Still another embodiment of the invention is a high-durabilitybismuth-free, lead-free, cadmium-free enamel composition comprising (a)a pigment, and (b) a frit portion, wherein the frit portion comprises,prior to firing: (i) 38-60 wt % SiO₂, (ii) 5.1-22.9 wt % B₂O₃, (iii)8.1-18 wt % TiO₂, (iv) 0.1-14.9 wt % ZnO, (v) 0.1-4.5 wt % Li₂O, (vi)0.1-18 wt % K₂O, and (vii) 1-7 wt % F, wherein the enamel compositionexhibits performance of chemical durability against wet throughdeterioration of at least 24 hours when tested in 0.1N H₂SO₄ at 80° C.

In yet another embodiment, the invention involves a substrate bearing afired coating, the fired coating comprising a frit portion, said fritportion comprising, prior to firing, (a) 38-60 wt % SiO₂, (b) 5.1-22.9wt % B₂O₃, (c) 8.1-18 wt % TiO₂, (d) 0.1-14.9 wt % ZnO, (e) 0.1-4.5 wt %Li₂O (f) 0.1-18 wt % K₂O, and (g) 1-7 wt % F.

Finally, an embodiment of the invention is a method of decorating aglass substrate comprising: (a) applying to a glass substrate an enamelcomposition comprising a solids portion, wherein the solids portioncomprises a frit portion, wherein the frit portion comprises, prior tofiring: (i) 38-60 wt % SiO₂, (ii) 5.1-22.9 wt % B₂O₃, (iii) 8.1-18 wt %TiO₂, (iv) 0.1-14.9 wt % ZnO, (v) 0.1-4.5 wt % Li₂O (vi) 0.1-18 wt %K₂O, and (vii) 1-7 wt % F, and (c) firing the substrate and enamelcomposition at a temperature sufficient to flow the enamel compositionto cause the enamel composition to at least partially adhere to theglass substrate.

The foregoing and other features of the invention are hereinafter morefully described and particularly pointed out in the claims, thefollowing description setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however, of but afew of the various ways in which the principles of the present inventionmay be employed.

DETAILED DESCRIPTION OF THE INVENTION

Enamel compositions of the invention include a glass frit portion, whichin turn includes a combination of the oxides of zinc, boron, silicon andtitanium, as well as fluoride ion.

In particular, the invention provides an enamel composition comprising asolids portion comprising a frit portion, wherein the frit portioncomprises, prior to firing: (a) 38-60 wt % SiO₂, (b) 5.1-22.9 wt % B₂O₃,(c) 8.1-18 wt % TiO₂, (d) 0.1-14.9 wt % ZnO, (e) 0.1-4.5 wt % Li₂O (f)0.1-18 wt % K₂O, and (g) 1-7 wt % F.

In another embodiment, the invention involves a method of decorating asubstrate comprising: (a) A method of decorating a substrate comprisingapplying to the substrate a coating of an enamel composition comprisinga solids portion, comprising a frit portion comprising, prior to firing:(i) 38-60 wt % SiO₂, (ii) 5.1-22.9 wt % B₂O₃, (iii) 8.1-18 wt % TiO₂,(iv) 0.1-14.9 wt % ZnO, (v) 0.1-3.5 wt % Li₂O (vi) 0.1-18 wt % K₂O, and(vii) 1-7 wt % F, and (b) firing the substrate and coating at atemperature sufficient to flow the enamel composition to cause theenamel composition to adhere to the substrate.

Still another embodiment of the invention is a high-durabilitybismuth-free, lead-free, cadmium-free enamel composition comprising (a)a pigment, and (b) a frit portion, wherein the frit portion comprises,prior to firing: (i) 38-60 wt % SiO₂, (ii) 5.1-22.9 wt % B₂O₃, (iii)8.1-18 wt % TiO₂, (iv) 0.1-14.9 wt % ZnO, (v) 0.1-4.5 wt % Li₂O, (vi)0.1-18 wt % K₂O, and (vii) 1-7 wt % F, wherein the enamel compositionexhibits performance of chemical durability against wet throughdeterioration of at least 24 hours when tested in 0.1N H₂SO₄ at 80° C.

In yet another embodiment, the invention involves a substrate bearing afired coating, the fired coating comprising a frit portion, said fritportion comprising, prior to firing, (a) 38-60 wt % SiO₂, (b) 5.1-22.9wt % B₂O₃, (c) 8.1-18 wt % TiO₂, (d) 0.1-14.9 wt % ZnO, (e) 0.1-4.5 wt %Li₂O (f) 0.1-18 wt % K₂O, and (g) 1-7 wt % F.

Finally, an embodiment of the invention is a method of decorating aglass substrate comprising: (a) applying to a glass substrate an enamelcomposition comprising a solids portion, wherein the solids portioncomprises a frit portion, wherein the frit portion comprises, prior tofiring: (i) 38-60 wt % SiO₂, (ii) 5.1-22.9 wt % B₂O₃, (iii) 8.1-18 wt %TiO₂, (iv) 0.1-14.9 wt % ZnO, (v) 0.1-4.5 wt % Li₂O (vi) 0.1-18 wt %K₂O, and (vii) 1-7 wt % F, and (c) firing the substrate and enamelcomposition at a temperature sufficient to flow the enamel compositionto cause the enamel composition to at least partially adhere to theglass substrate.

The components of the inventive compositions, articles and methods aredetailed hereinbelow. Compositional percentages are by weight. Certainembodiments of the invention are envisioned where at least somepercentages, temperatures, times, and ranges of other values arepreceded by the modifier “about.” All compositional percentages are byweight and are given for a blend prior to firing. Details on eachingredient follow.

Frit (Glass) Component. The principal glass and enamel compositionsherein include SiO₂, B₂O₃, TiO₂, ZnO, Li₂O, K₂O and F₂. In particular,broad and preferred embodiments of the glass and enamel compositionsherein are detailed below. The glass frit compositions herein includeSiO₂: broadly 38-60%, preferably 41-51% and more preferably 45-50%;B₂O₃: broadly 5.1-22.9%; preferably 6-17% and more preferably 8-15%;TiO₂: broadly 8.1-18 wt %, preferably 8.5-13%, more preferably 11-15%;ZnO: broadly 0.1-14.9%; preferably 5.1-13%; more preferably 8-12%; Li₂O:broadly 0.1-4.5%, preferably 0.1-3%, more preferably 0.5-2.5%; K₂O:broadly 0.1-18%; preferably 1-7.9%, more preferably 1.7-4%; and F:broadly 1-7%, preferably 1.5-6%, more preferably 2-5%. Alternately, theTiO₂ content may be 10.5-18 wt %, preferably 11-17 wt % and morepreferably 11.5-16.5 wt %. Alternately, the SiO₂ content may be20.1-22.9%, preferably 20.5-22.5%. Alternately, the ZnO content may be13.1-14.9%, preferably 13.3-14.7%.

Other embodiments are possible, using, for example, a combination ofranges of oxides indicated hereinabove as “broad,” “preferred” and “morepreferred” in various combinations, so long as such combinations ofranges can add up to 100 wt %. For example, 38-60 wt % SiO₂; 8-15 wt %B₂O₃; 8.5-13 wt % TiO₂ 8-12 wt % ZnO, 0.1-4.5 wt % Li₂O, 0.1-18 wt %K₂O, and 1-7 wt % F. Another possible embodiment is 41-51 wt % SiO₂,5.1-22.9 wt % B₂O₃, 11-15 wt % TiO₂, 5.1-13 wt % ZnO, 0.1-3 wt % Li₂O,1-7.9 wt % K₂O and 1-7 wt % F. Yet another is 38-60 wt % SiO₂, 5.1-22.9wt % B₂O₃, 10.5-18 wt % TiO₂, 0.1-14.9 wt % ZnO, 0.1-4.5 wt % Li₂O,0.1-18 wt % K₂O, and 1-7 wt % F. Another embodiment is 38-60 wt % SiO₂,6-17% wt % B₂O₃, 10.5-18 wt % TiO₂, 0.1-14.9 wt % ZnO, 0.1-4.5 wt %Li₂O, 0.1-18 wt % K₂O, and 1-7 wt % F. Another possible embodimentcomprises 38-60 wt % SiO₂, 5.1-22.9 wt % B₂O₃, 11-15 wt % TiO₂, 0.1-14.9wt % ZnO, 0-4.5 wt % Li₂O, 0.1-18 wt % K₂O and 1-7 wt % F, wherein thefrit is substantially free of oxides of tantalum. Still othercombinations are possible, as will be evident by examining the precedingparagraph.

Secondary, optional, oxides may be added to frits according to theformulations in the preceding two paragraphs in the following weightpercentages: Al₂O₃, 0.1-1.9%, preferably 0.1-0.95, more preferably0.1-0.8%; ZrO₂: 0.1-4%, preferably 0.1-1.5%, more preferably 0.1-0.8%;and Na₂O: 0.1-13%, preferably 5-12%, more preferably 8-11%.

Additional oxides can be added to any previously described embodiment,singly, or in any combination, up to the noted weight percentage: Cs₂O:2%; MgO: 5%; CeO₂: 5%; MnO: 10%; CuO: 5%; NiO 5%; SnO: 10%; P₂O₅: 5%;V₂O₅: 10%; La₂O₃: 5%; Pr₂O₃: 5%; In₂O₃: 5%; Fe₂O₃: 10%; Cr₂O₃: 5%; CoO:5%; Nb₂O₅: 4; WO₃: 4; and MoO₃: 4. In a preferred embodiment, the fritportions of the enamel compositions herein further comprise at least oneof the noted additional oxides where the range has a lower bound of0.1%. The frit portions of the enamel compositions herein may alsoinclude 0.1-4.9% Bi₂O₃, but this is not preferred. It is also preferredthat the frits herein, and the overall enamel compositions herein, aresubstantially free of, and preferably devoid of oxides of antimony andoxides of tantalum.

As can be seen above, the composition of the glass frits useful in thisinvention can be adapted over a broad range of oxide compositions.Glasses may be formulated according to the principal glass and enamelcompositions above, together with, optionally one or more secondary oradditional oxides. The glass and enamel compositions herein typicallycontain low amounts of PbO, CdO and Bi₂O₃, i.e., less than 5 wt % ofeach, preferably less than 1 wt % of each, more preferably less than 0.5wt % of each, and even more preferably, less than 0.1 wt % of each. Mostpreferably, the glass and enamel compositions herein are substantiallyfree of, and preferably devoid of intentionally added PbO, CdO, andBi₂O₃. Still more preferably, the glass frit compositions herein and theenamels made therefrom are absolutely devoid of lead, cadmium, andbismuth in any form. However, certain embodiments not involving food orbeverage storage may intentionally include oxides of lead, cadmium,bismuth, or any combination thereof.

Sulfide glass frits are glass frits that contain a metal sulfidecomponent. Certain embodiments of the invention include sulfide ionsprovided by elemental sulfur or metallic sulfides. Exemplary sulfideglass frits are disclosed in U.S. Pat. No. 5,350,718 to Antequil et al.,which is hereby incorporated by reference. Exemplary sulfides in suchfrits include ZnS, MnS, FeS, CoS, NiS, Cu₂S, CdS, Sb₂S₃ and Bi₂S₃. Inparticular, the frit portion may further comprise sulfur or a metallicsulfide, or combinations thereof, so as to provide an amount of sulfurto the frit portion not exceeding 4 wt %, all percentages prior tofiring. The presence of the sulfides disclosed herein can have abeneficial effect on the glass coatings herein as they act as reducingagents which can prevent or minimize silver migration from a conductivesilver metal trace into a glass substrate or coating. A glass componentcontaining both oxide and sulfide frits are also envisioned.

Broadly, the glass frits and enamels useful herein have melting pointsin the range of about 1000° F. to 1400° F., or any intermediatetemperature such as 1030° F., 1040° F., 1050° F., 1060° F., 1080° F.,1110° F., 1150° F., 1190° F., 1200° F., 1210° F., 1250° F., 1275° F.,1300° F., 1325° F., 1350° F., and 1375° F., and various of the frits maybe effectively fired at those temperatures. Preferably, the glass fritsherein can be fired at 1000-1250° F., more preferably at 1020-1200° F.,still more preferably at about 1030-1150° F., and most preferably atabout 1040-1100° F.

Generally, the glass frits are formed in a known manner, for example,blending the starting materials (oxides and/or sulfides) and meltingtogether at a temperature of about 1000 to about 1400° C. (about 1830 toabout 2550° F.) for about 45 to about 75 minutes to form a molten glasshaving the desired composition. The molten glass formed can then besuddenly cooled in a known manner (e.g., water quenched) to form a frit.The frit can then be ground using conventional milling techniques to afine particle size, from about 1 to about 8 microns, preferably 2 toabout 6 microns, and more preferably about 3 to about 5 microns.

Crystalline Material. Crystalline materials may be included along withthe frit compositions herein to promote crystallization (i.e.,crystallization seeds). Crystalline materials useful herein include zincsilicates, zinc borates, zinc titanates, silicon zirconates, aluminumsilicates, calcium silicates, and combinations thereof. The crystallinematerials may include, without limitation, Zn₂SiO₄, 2ZnO.3TiO₂, ZnTiO₃,ZnO.B₂O₃, 3ZnO.B₂O₃, 5ZnO.2B₂O₃, and Al₂SiO₅. The Ruderer U.S. Pat. No.5,153,150 and Sakoske U.S. Pat. No. 5,714,420 patents noted hereinaboveprovide further information on crystalline materials. Preferredcrystalline materials include zinc silicates such as Zn₂SiO₄ and zincborosilicates such as ZnO.B₂O₃. Specific examples of seed materials usedherein include product numbers 2077 (bismuth silicate seed material) and2099 (zinc silicate seed material) manufactured by Ferro Glass and ColorCorporation of Washington, Pa. The enamels herein may include 0.1-15 wt%, preferably about 0.5-10 wt %, and more preferably 1-5 wt % of atleast one crystalline material.

Decoration and Glass Forming. A glass substrate may be colored ordecorated by applying any enamel composition described herein to atleast a portion of a substrate, for example, a glass substrate such as aglass sheet, or automotive glass, (i.e., windshield). An enamelcomposition may, but need not, be applied in the form of a paste asdisclosed herein.

In particular, a method of decorating a glass substrate comprising: (a)applying to a glass substrate an enamel composition comprising a solidsportion, wherein the solids portion comprises a frit portion, whereinthe frit portion comprises, prior to firing: (i) 38-60 wt % SiO₂, (ii)5.1-22.9 wt % B₂O₃, (iii) 8.1-18 wt % TiO₂, (iv) 0.1-14.9 wt % ZnO, (v)0.1-4.5 wt % Li₂O (vi) 0.1-18 wt % K₂O, and (vii) 1-7 wt % F, and (c)firing the substrate and enamel composition at a temperature sufficientto flow the enamel composition to cause the enamel composition to atleast partially adhere to the glass substrate. The enamel compositionmay be applied to the entire surface of a glass substrate, or to only aportion thereof, for example the periphery.

The method may include a glass forming step whereby the glass substrateis heated to an elevated temperature and subjected to a forming pressureto bend the glass substrate. In particular, bending the glass substratemay involve heating the glass substrate to which has been applied the toan elevated temperature, of, for example, at least about 570° C., atleast about 600° C., at least about 625° C., or at least about 650° C.Upon heating, the glass is subjected to a forming pressure, e.g.,gravity sag or press bending in the range of 0.1 to 5 psi, or 1-4 psi,or typically about 2-3 psi, with a forming die.

Organic Vehicle. When applied by procedures requiring one, such asscreen printing, the foregoing solid ingredients may be combined with anorganic vehicle to form a glass enamel composition, which is a paste.The paste in general contains 60-90 wt % solids, (a paste ratio as notedin the Examples of 1.5:1 to 9:1), preferably 65-85%, more preferably70-80 wt %, as above described and 10-40% of an organic vehicle,preferably 15-35%, more preferably 20-30%. The viscosity of the paste isadjusted so that it can be screen-printed, roll coated, sprayed, orotherwise applied in a desired manner onto the desired substrate. Otherpreferred paste ratios are about 3.5:1 to 4.5:1, and more preferablyabout 3.7:1 to 4.4:1.

The organic vehicle comprises a binder and a solvent, which are selectedbased on the intended application. It is essential that the vehicleadequately suspend the particulates (i.e., frit, pigment, crystallinematerial) and burn off completely upon firing. In particular, bindersincluding methyl cellulose, ethyl cellulose, and hydroxypropylcellulose, and combinations thereof, may be used. Suitable solventsinclude propylene glycol, diethylene glycol butyl ether; 2,2,4-trimethylpentanediol monoisobutyrate (Texanol™); alpha-terpineol; beta-terpineol;gamma terpineol; tridecyl alcohol; diethylene glycol ethyl ether(Carbitol™), diethylene glycol butyl ether (Butyl Carbitol™); pine oils,vegetable oils, mineral oils, low molecular weight petroleum fractions,tridecyl alcohols, and synthetic or natural resins and blends thereof.Surfactants and/or other film forming modifiers can also be included.The solvent and binder may be present in a weight ratio of about 50:1 toabout 20:1. The preferred vehicle is a combination of Butyl Carbitol™(diethylene glycol monobutyl ether) and ethyl cellulose in a weightratio of about 200:1 to 20:1, preferably 50:1 to about 20:1, morepreferably about 40:1 to about 25:1.

In general, the enamel pastes are viscous in nature, with the viscositydepending upon the application method to be employed and end use. Forpurposes of screen-printing, viscosities ranging from 10,000 to 80,000,preferably 15,000 to 35,000 centipoise, and more preferably 18,000 to28,000 centipoise at 20° C., as determined on a Brookfield Viscometer,#29 spindle at 10 rpm, are appropriate.

Pigments. In certain embodiments, the glass frit can be combined with apigment, such as a mixed metal oxide pigment. When used, such pigmentsgenerally constitute no greater than about 30 wt %, preferably 0.1-30%,more preferably 1-25 wt %, still more preferably 2-20 wt %, of the glassenamel compositions herein, depending upon the range of color, gloss,and opacity (i.e., transmittance) desired.

Keeping in mind the general preference for completely lead-free,cadmium-free, and bismuth-free compositions for food and beverages,useful pigments may come from several of the major classifications ofcomplex inorganic pigments, including corundum-hematite, olivine,priderite, pyrochlore, rutile, spinel, and spinel, though othercategories such as baddeleyite, borate, garnet, periclase, phenacite,phosphate, sphene and zircon may be suitable in certain applications.Oxides of the metals cobalt, chromium, manganese, praseodymium, iron,nickel, and copper are often useful. In particular, specific pigmentsinclude cobalt silicate blue olivine Co₂SiO₄; nickel barium titaniumprimrose priderite 2NiO:3BaO:17TiO₂; nickel antimony titanium yellowrutile (Ti,Ni,Nb)O₂; nickel niobium titanium yellow rutile (Ti,Ni,Nb)O₂;nickel tungsten yellow rutile (Ti,Ni,W)O₂; chrome antimony titanium buff(Ti,Cr,Sb)O₂; chrome niobium titanium buff rutile (Ti,Cr,Nb)O₂; chrometungsten titanium buff rutile (Ti,Cr,W)O₂; manganese antimony titaniumbuff rutile (Ti,Mn,Sb)O₂; titanium vanadium grey rutile (Ti,V,Sb)O₂;manganese chrome antimony titanium brown rutile (Ti,Mn,Cr,Sb)O₂;manganese niobium titanium brown rutile (Ti,Mn,Nb)O₂; cobalt aluminateblue spinel CoAl₂O₄; zinc chrome cobalt aluminum spinel(Zn,Co)(Cr,Al)₂O₄; cobalt chromate blue-green spinel CoCr₂O₄; cobalttitanate green spinel Co₂TiO₄; iron chromite brown spinel Fe(Fe,Cr)₂O₄;iron titanium brown spinel Fe₂TiO₄; nickel ferrite brown spinel NiFe₂O₄;zinc ferrite brown spinel (Zn,Fe)Fe₂O₄; zinc iron chromite brown spinel(Zn,Fe)(Fe,Cr)₂O₄; copper chromite black spinel CuCr₂O₄; iron cobaltchromite black spinel (Co,Fe)(Fe,Cr)₂O₄; chrome iron manganese brownspinel (Fe,Mn)(Cr,Fe)₂O₄; chrome iron nickel black spinel(Ni,Fe)(Cr,Fe)₂O₄; and chrome manganese zinc brown spinel(Zn,Mn)(Cr₂O₄). Only in applications where lead is permitted (i.e.,other than food or beverage containers, tableware, etc.), leadantimonite yellow pyrochlore (Pb₂Sb₂O₇) or other lead-containingpigments may be used. Commercially available examples of suitablepigments are available from Ferro Glass and Color Corporation, such as2991 pigment (copper chromite black), 2980 pigment (cobalt chromium ironblack), 2987 pigment (nickel manganese iron chromium black), and O-1776pigment (black). In some embodiments, pigments free from Co, Cu, Cr, Niand the like such a 10201 black (bismuth manganate) would also besuitable. In a preferred embodiment, no bismuth is present in thepigment.

Especially preferred are pigments having the following Ferro Corporationproduct numbers and formulas: K393 (CuCrMn), V792(NiMnCrFe),2503(CdSeS), 2336(CoAl), and 2501(CdSeS), however this is in the contextof the overall preference for enamels that are free of intentionallyadded lead, cadmium and bismuth.

Metal. Certain embodiments of the enamels herein may advantageouslyinclude one or more metals in relatively small amounts. For example, theenamel may include a metal such as silicon, added separately from anyoxide, in an amount of 0.1 to 5 wt %, preferably 0.5 to about 4.5 wt %more preferably 1 to 4 wt %. Silicon metal is a reducing agent whichprevents or minimizes the extent of oxidation, especially of silvermetal in conductive traces, however sulfides also act as reducingagents. Such reducing agents have the desired effect of preventing orminimizing the extent of silver migration into a glass substrate orcoating. Other metals that enhance the desired properties of the glassenamels herein or at a minimum, do not degrade such desired properties,are also envisioned herein. For example, metals from which the oxidesused in the frits or pigments herein may be used, keeping in mind thepreferences for low or essentially zero levels of heavy metals such aslead, cadmium, and bismuth.

The solids portion of the enamel is considered to be the glass fritportion, the pigment, the crystallization material, and the metal, takentogether.

Properties. The glass articles herein are coated in order to impartdesired properties to the article. The properties of acid resistance,heavy metal release, color, gloss, and light transmittance, characterizethe final finished products are detailed hereinbelow.

Acid Resistance. The glass and enamel compositions herein, and the firedglass, ceramic, and enamel coatings obtained by the firing thereof areoften used in harsh environments, including, for example, automotive orarchitectural glass, institutional table ware, and others.

Heavy Metal Release. Because the inventive glass and enamel compositionsherein may be used to decorate glassware for preparing, serving, andstoring food, it is important that such compositions contain extremelylow concentrations of toxic heavy metals, such as lead and cadmium.Further, in the in the inevitable event that the glass and enamelcompositions contains a small portion of such toxic metals, it isimportant that the glass and enamel compositions do not release theheavy metals, or do so only at very low levels. For example, it is anadvantage of the glass and enamel compositions herein release less than100 ppm of heavy metals of any kind when subjected to a strong detergentattack as set forth in DTM 77, described hereinbelow. It is morepreferred that the glass and enamel compositions release less than 75ppm, and even more preferred when less than 50 ppm is released. It isstill more preferred that less than 25 ppm be released.

Dispersing Surfactant. A dispersing surfactant assists in pigmentwetting, when an insoluble particulate inorganic pigment is used. Adispersing surfactant typically contains a block copolymer with pigmentaffinic groups. For example, surfactants sold under the Disperbyk® andByk® trademarks by Byk Chemie of Wesel, Germany, such as Disperbyk 162and 163, which are solutions of high molecular weight block copolymerswith pigment affinic groups, and a blend of solvents (xylene,butylacetate and methoxypropylacetate). Disperbyk 162 has these solventsin a 3/1/1 ratio, while the ratio in Disperbyk 163 is 4/2/5. Disperbyk140 is a solution of alkyl-ammonium salt of an acidic polymer in amethoxypropylacetate solvent.

Rheological Modifier. A rheological modifier is used to adjust theviscosity of the green pigment package composition. A variety ofrheological modifiers may be used, including those sold under the Byk®,Disperplast®, and Viscobyk® trademarks, available from Byk Chemie. Theyinclude, for example, the BYK 400 series, such as BYK 411 and BYK 420,(modified urea solutions); the BYK W-900 series, (pigment wetting anddispersing additives); the Disperplast series, (pigment wetting anddispersing additives for plastisols and organosols); and the Viscobykseries, (viscosity depressants for plastisols and organosols).

Flow aid. A flow aid is an additive used to control the viscosity andrheology of a pigment or paste composition, which affects the flowproperties of liquid systems in a controlled and predictable way.Rheology modifiers are generally considered as being eitherpseudoplastic or thixotropic in nature. Suitable surfactants hereininclude those sold commercially under the Additol®, Multiflow®, andModaflow® trademarks by UCB Surface Specialties of Smyrna, Ga. Forexample, Additol VXW 6388, Additol VXW 6360, Additol VXL 4930, AdditolXL 425, Additol XW 395, Modaflow AQ 3000, Modaflow AQ 3025, ModaflowResin, and Multiflow Resin.

Adhesion promoter. Adhesion promoting polymers are used to improve thecompatibility between a polymer and a filler. Suitable adhesionpromoters include those sold by GE Silicones of Wilton, Conn. under theSilquest®, CoatOSil®, NXT®, XL-Pearl™ and Silcat® trademarks. Examplesinclude the following product numbers, sold under the Silquest®trademark: A1101, A1102, A1126, A1128, A1130, A1230, A1310, A162, A174,A178, A187, A2120. For example, Silquest® A-187 is(3-glycidoxypropyl)trimethoxysilane, which is an epoxysilane adhesionpromoter. The inventors herein have found that aromatic epoxiescrosslinked with amines or amides produced unacceptable results. Silanessold by Degussa AG of Düsseldorf, Germany, under the Dynasylan®trademark are also suitable. Most preferred herein is Silquest A187.

Stabilizers. Light or UV stabilizers are classified according to theirmode of action: UV blockers—that act by shielding the polymer fromultraviolet light; or hindered amine light stabilizers (HALS)—that actby scavenging the radical intermediates formed in the photo-oxidationprocess. The compositions of the invention comprise about 0.1 to about 2wt % of a light stabilizer, preferably about 0.5 to about 1.5%, andfurther comprise about 0.1 to about 4 wt % of a UV blocker, preferablyabout 1 to about 3%.

Light stabilizers and UV blockers sold under the Irgafos®, Irganox®,Irgastab®, Uvitex®, and Tinuvin® trademarks by from Ciba SpecialtyChemicals, Tarrytown, N.Y., may be used, including product numbers 292HP, 384-2, 400, 405, 411L, 5050, 5055, 5060, 5011, all using the Tinuvintrademark. Suitable UV blocking agents include Norbloc 7966 (2-(2′hydroxy-5′ methacryloxyethylphenyl)-2H-benzotriazole); Tinuvin 123(bis-(2,2,6,6-tetramethyl-1-(octyloxy)-4-piperidinyl)ester); Tinuvin 99(3-(2H-benzotriazole-2-yl)5-(1,1-dimethylethyl)-4-hydroxybenzenepropanoic acid, C7-9-branched alkyl esters)Tinuvin 171 (2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methyl-phenol).Products sold under the Norbloc® trademark are available from JanssenPharmaceutica of Beerse, Belgium.

Suitable hindered amine light stabilizers (HALS) are sold by theClariant Corporation, Charlotte, N.C., under the Hostavin® trademark,including Hostavin 845, Hostavin N20, Hostavin N24, Hostavin N30,Hostavin N391, Hostavin PR31, Hostavin ARO8, and Hostavin PR25. HALS areextremely efficient stabilizers against light-induced degradation ofmost polymers. They do not absorb UV radiation, but act to inhibitdegradation of the polymer, thus extending its durability. Significantlevels of stabilization are achieved at relatively low concentrations.The high efficiency and longevity of HALS are due to a cyclic processwherein the HALS are regenerated rather than consumed during thestabilization process. They also protect polymers from thermaldegradation and can be used as thermal stabilizers.

Examples. The following compositions represent exemplary embodiments ofthe invention. They are presented to explain the invention in moredetail, and do not limit the invention. High durability glass fritcompositions according to the present invention are given in Table 1,Frits A-J. Comparative frits are given at the left side of Table 1 (3columns). The thermal expansion coefficient was determined from roomtemperature to 300° C. using an Orton model 1000R dilatometer. The glasstransition temperature is Tg and the dilatometric softening point is Td.The firing temperature determination is described herein. The “firingtemperature” is the temperature where the frit particles begin to meltand sinter together upon heating. The room temperature chemicaldurabilities were determined as described hereinbelow for 4% aceticacid, 10% citric acid, and 10% hydrochloric acid solutions.

Heavy Metal (cadmium) release of selected enamels in Table 1 is alsopresented. Sample automotive windshield enamels were also made usingthese compositions as presented in Table 2. The paste ratio is theweight ratio of solid constituents (glass frits, pigments, crystallinematerials, metals) to organic vehicle. The minimum fire of the enamel isdetermined as described below. The acid test using immersion in 0.1Nsulfuric acid at 80° C. is commonly called the Toyota test. Results arereported in hours where The wet through method was used to determinepoint of failure as described below. Conventional low firing zinc-basedenamels have not been able to survive wet through for more than 4 hoursof exposure to 0.1N sulfuric acid at 80° C.

TABLE 1 Frit formulations in wt %, firing temperatures, data on acidresistance and heavy metal release. Compar- Compar- ative ativeComparative Formula Frit 1 Frit 2 Frit 3 Frit A Frit B Frit C Frit DFrit E Frit F Frit G Frit H Frit I Frit J Oxide Nb₂O₅ 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 CeO₂ 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 SiO₂ 20.52 20.31 38.8245.02 44.50 42.04 39.74 45.28 40.87 47.72 47.58 41.01 43.51 TiO₂ 0.001.64 7.65 9.51 9.41 8.89 12.38 9.57 12.73 12.47 10.06 8.89 10.71 ZrO₂1.15 7.93 0.00 0.67 0.67 0.63 0.59 0.68 0.61 0.00 0.71 1.27 0.67 Al₂O₃3.26 1.64 0.00 0.66 0.65 0.62 0.58 0.66 0.60 1.41 0.70 0.33 0.65 B₂O₃30.09 27.17 9.69 14.39 14.22 13.44 12.70 14.47 13.07 16.21 15.21 22.5614.24 Bi₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 1.51 0.00 0.00 0.00 0.00 0.000.00 SO₃ 0.00 0.00 0.00 0.00 1.15 1.14 1.08 0.00 0.00 0.00 0.00 0.000.00 CaO 0.00 5.39 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 PbO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 ZnO 33.37 24.63 34.38 11.12 10.99 10.59 10.01 11.18 10.09 0.54 6.077.22 13.36 K₂O 0.00 0.00 6.06 2.36 2.33 17.57 16.60 0.67 17.08 5.01 2.493.12 1.22 Li₂O 0.00 0.00 1.61 1.95 1.93 1.82 1.72 1.96 1.77 2.17 2.061.82 1.76 Na₂O 11.61 10.26 1.80 10.83 10.70 0.00 0.00 12.01 0.00 11.2111.44 9.76 10.41 F₂ 0.00 1.02 0.00 3.49 3.45 3.26 3.08 3.51 3.17 3.263.69 4.02 3.46 Total 100 100 100 100 100 100 100 100 100 100 100 100 100TEC × 10⁻⁷ in/ 75.0 80.0 69.0 87.3 91.0 81.0 86.0 85.9 93.0 99.7 96.7 9286.5 in ° C. Tg ° C. 476 — 485 425 436 480 458 423 440 460 430 410 420Td ° C. 520 — 534 475 495 530 515 491 496 505 489 460 485 Fire Temp 10501110 1110 1040 1050 1100 1060 1035 1030 1080 1070 1030 1040 ° F.  4%Acetic 5 — 1 2 3 1 1 2 1 1 1 2 2 10% Citric 6 5 1 4 3 1 2 4 4 1 2 4 410% HCl — — 4 4 1 1 1 4 4 1 2 5 4 HMR [Cd] removed 74.0 200 3.1 — — —3.7 3 1.4 1.3 5.6 8.2 PPM

TABLE 2 Enamel formulations in wt %, firing data, and acid resistanceperformance data for pastes made with selected frits from table 1.Comparative Comparative Comparative Glass Used Enamel 1 Enamel 2 Enamel3 Enamel A Enamel B Enamel C Enamel D Comparative Frit 1 75.00Comparative Frit 2 75.00 Comparative Frit 3 75.00 Glass A 75.00 Glass B73.70 Glass C 74.70 Glass D 74.70 2099 3.40 3.40 3.40 3.40 5.00 3.003.00 2077 1.00 1.00 K393 20.00 20.00 20.00 20.00 O-1776B 19.00 19.0019.00 V792 2.30 2.30 2.30 Si Metal 1.60 1.60 1.60 1.60 100.0 100.0 100.0100.0 100.0 100.0 100.0 MIN FIRE ° F. 1100 1110 1170 1120 1150 1180 1130Paste Ratio 4.4 4.2 3.75 4.0 3.7 3.7 3.7  4% Acetic acid 6 5 3 2 1 1 110% Citric acid 7 7 4 3 2 1 1 10% HCl acid 6 6 4 3 3 1 3 0.1N H₂SO₄ at80° C. <1 <1 1-2 34-37 50-58 45-49 41-45 (hours)

The testing procedures used herein are as follows, starting with theFiring Temperature Estimate of the frit (“Min Fire” in table 2). Ascreen printable paste is made by blending 4 g±0.1 grams of test fritwith pine oil. After a ten-minute pre-heat at 800° F., the trials arethen rapidly transferred to a second furnace at a temperature below theexpected firing temperature for the frit for 15 minutes. After 15minutes in the second furnace, the trials are removed and cooled. Thiscycle is repeated (at higher temperatures) until the printed fritparticles become sintered together and cannot be scratched away. Oncethe “firing temperature” has been determined, an underfire of 10° F.below the “firing temperature” is made for confirmation. The Min Fire ofthe enamel, describes the method for determining the minimum temperaturenecessary to adequately fuse a ceramic glass enamel to a glasssubstrate. A screen printable glass-ceramic enamel paste is made, and a4″×4″ test plate is printed and the solvent dried on a hot plate at 200°F. The test plate is placed into the pre-heat furnace, which has alreadybeen pre-set at 800° F. and left in the furnace for 6 minutes. Purposeof the pre-heat is to allow the glass test plate and metal firing rackto heat up while also allowing the majority of the organic vehicle to beburnt off before the regular firing. After the 6 minutes time hasexpired, the test plate is quickly transferred from the pre-heat furnaceto a second furnace, previously set at a Min Fire temperature estimateand fired for 4 minutes. After the 4-minute fire, the test plate isremoved and cooled to room temperature.

After cooling, the fired maturity of the enamel is checked by using awet through test. This test involves placing a drop of water on theindex finger tip and pressing against the surface of the enamel, thenviewing through the glass to see if the water is absorbed through theenamel. The observer will notice either a water spot or mark if wettingthrough to the substrate occurs. A black felt tip marker can also beused for marking the enamel surface and determining whether absorption(wetting) occurs. If wetting is observed, increase the second Min Fireestimate furnace temperature by 10° F. & repeat. Continue at 10°increments until wetting is no longer observed. If wetting is notobserved, decrease the second Min Fire estimate furnace temperature by10° F. and repeat. Continue at 10° increments until wetting is observed.Minimum firing temperature for a glass enamel is described as thattemperature, at 4 minutes, in which the enamel no longer exhibitswetting, thus providing fusing and development of the glass enamel tothe glass substrate.

Acid Test Resistance to 10% Citric Acid at Room Temperature, ASTMC-724-91. A visual assessment of the resistance of a glass enamel orfrit coating to 10% citric acid at room temperature is made of anyresidual stain after exposure to the acid solution for 15 minutes. Thesame test is conducted with respect to a 4 wt % solution of acetic acidat room temperature for a one-minute exposure, and a 10 wt % solution ofhydrochloric acid at room temperature for a ten-minute exposure. Therating scale is based upon the following:

Grade 1—No apparent attack

Grade 2—Appearance of iridescence or visible stain on the exposedsurface when viewed at an angle of 45°, but not apparent when viewed atangles less than 30°.

Grade 3—A definite stain which does not blur reflected images and isvisible at angles less than 30°.

Grade 4—Definite stain with a gross color change or strongly iridescentsurface visible at angles less than 30° and which may blur reflectedimages.

Grade 5—Surface dull or matte with chalking possible.

Grade 6—Significant removal of enamel with pinholing evident.

Grade 7—Complete removal of enamel in exposed area.

Heavy Metal Release. Standard test samples are formulated, fired, andaged. The trials are placed in a 4000 cc stainless steel beakercontaining a solution consisting of: 2000 cc distilled water and 6 gramsof Super Soilax detergent. During the detergent “aging” exposure priorto HMR testing, the entire trial must be submersed in the solution. Thebeaker with fired trials is then placed in a constant temperature waterbath at 95° C. for 24 hours. After the trials have been exposed to theheated solution for 24 hours, the beaker is removed from the water bath,and the trials are removed from the beaker. The trials are immediatelyrinsed with tap water, while rubbing the exposed enamel surface toremove any residue. The lead and cadmium release values are obtained byatomic absorption spectrophotometer, and reported as parts per million(PPM).

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and illustrative example shown anddescribed herein. Accordingly, various modifications may be made withoutdeparting from the spirit or scope of the general invention concept asdefined by the appended claims and their equivalents.

1. An opaque, fired enamel composition that is lead-free, cadmium-free,bismuth-free, tantalum-free and antimony-free, the enamel compositioncomprising, prior to firing an organic vehicle and a solids portion,wherein the solids portion comprises a frit portion, wherein the fritportion comprises, prior to firing: a. 10-80 wt % of a glass frit, thefrit comprising i. 39.74 to 47.72 wt % SiO₂, ii. 12.7 to 22.56 wt %B₂O₃, iii. 8.89 to 12.73 wt % TiO₂, iv. 0.54 to 13.36 wt % ZnO, v. 1.72to 2.17 wt % Li₂O vi. 0.67 to 17.57 wt % K₂O, and vii. 3.08 to 4.02 wt %F, viii. 0.58 to 1.41 wt % Al₂O₃, ix. 0 to 1.27 wt % ZrO₂, x. 0 to 12.01wt % Na₂O, b. a separate and distinct addition of 0.1-30 wt % pigment,and c. 0.1-15 wt % of a crystalline material selected from the groupconsisting of zinc borates, zinc silicates, zinc titanates, aluminumsilicates, and combinations thereof, wherein, after firing, the enamelcomposition exhibits performance of chemical durability against wetthrough deterioration of at least 24 hours when tested in 0.1N H₂SO₄ at80° C.
 2. The enamel of claim 1 further comprising (d) 0.1 to 5 wt % ofa metal.
 3. The enamel composition of claim 1, wherein the frit portionfurther comprises sulfur or a metallic sulfide, or combinations thereof,so as to provide an amount of sulfur to the frit portion not exceeding 4wt %, all percentages prior to firing.
 4. The enamel composition ofclaim 1, wherein the frit portion further comprises at least oneselected from the group consisting of: (a) 0.1-2 wt % Cs₂O, (b) 0.1-5 wt% MgO, (c) 0.1-5 wt % CeO₂, (d) 0.1-10 wt % MnO, (e) 0.1-5 wt % CuO, (f)0.1-5 wt % NiO, (g) 0.1-10 wt % SnO, (h) 0.1-5 wt % P₂O₅, (i) 0.1-10 wt% V₂O₅, (j) 0.1-5 wt % La₂O₃, (k) 0.1-5 wt % Pr₂O₃, (l) 0.1-5 wt % Y₂O₃,(m) 0.1-5 wt % In₂O₃, (n) 0.1-10 wt % Fe₂O₃, (O) 0.1-5 wt % Cr₂O₃, (q)0.1-5 wt % CoO, (q) 0.1-4 wt % Nb₂O₅, (r) 0.1-4 wt % WO₃, (s) 0.1-4 wt %MoO₃, and combinations thereof.
 5. The opaque, fired enamel compositionof claim 1, wherein the enamel composition has a minimum firingtemperature of no greater than 1250° F.
 6. The opaque, fired enamelcomposition of claim 1, wherein the enamel composition has a minimumfiring temperature of no greater than 1180° F.
 7. The enamel compositionof claim 2, further comprising a reducing compound to reduce the metalin the composition or prevent oxidation of metals in the enamelcomposition to control silver migration into the substrate.
 8. Theenamel composition of claim 7, wherein the reducing compounds areselected from the group consisting of silicon metal, zinc sulfide,metallic sulfides, and combinations thereof.
 9. A substrate bearing afired coating, the coating having a minimum firing temperature of nogreater than 1180° F., wherein the fired coating comprises a fritportion, said frit portion comprising, prior to firing, a. 39.74 to47.72 wt % SiO₂, b. 12.7 to 22.56 wt % B₂O₃, c. 8.89 to 12.73 wt % TiO₂,d. 0.54 to 13.36 wt % ZnO, e. 1.72 to 2.17 wt % Li₂O f. 0.67 to 17.57 wt% K₂O, and g. 3.08 to 4.02 wt % F, h. 0.58 to 1.41 wt % Al₂O₃, i. 0 to1.27 wt % ZrO₂, and j. 0 to 12.01 wt % Na₂O, the fired coatingexhibiting performance of chemical durability against wet throughdeterioration of at least 24 hours when tested in 0.1N H₂SO₄ at 80° C.